These are a few quick notes to self, rather than a cogent thesis. I want to get this out while it’s still fresh, and I want to lower my own mental barrier to publishing here.

I’ve been thinking about test coverage recently, inspired by conversations that followed DRMacIver …

We use quay.io a fair bit at work—all our internal Docker images are stored there. I like it a lot, but the website makes it really hard to see who can access your repositories.

In particular, if someone ever leaves your organization, you have to click through all …

I am pleased to announce that the recent TLS certificate problems and outages to jml.io have been fully resolved.

Here are some notes on what happened and what I did about it.

Hank Green recently shared the embarrassing secret to his productivity, which he summarises as:

Everything creative I do, I do my best to get it 80% of the way to as good as I can make it and go no further. I just don’t try to get it to …

I was going to write a post about how knowing some abstract algebra can help you write clearer programs.

Then I saw Eugenia Cheng’s excellent talk, Category Theory in Everyday Life, which was a keynote at Haskell Exchange 2017.

It’s excellent. She says what I wanted to say …

Porting SPAKE2 from Python to Haskell helped me understand how SPAKE2 worked, and a large part of that is due to specific features of Haskell.

Last post, I discussed how I found myself implementing SPAKE2 in Haskell. Here, I want to discuss what SPAKE2 is, and why you might care.

There’s a joke about programmers that’s been doing the rounds for the last couple of years:

We do these things not because they are easy, but because we thought they would be easy.

This is about how I became the butt of a tired, old joke.

My friend …

Last October, I announced servant-template, a cookiecutter template for creating production-ready Haskell web services.

Almost immediately after making it, I wished I had something for building command-line tools quickly. I know stack comes with a heap of them, but:

• it’s hard to predict what they’ll do
• adding a …

Late last year, my friend Tom tried to convince me that writing REST APIs was boring and repetitive and that I should give this thing called GraphQL a try.

I was initially sceptical. servant, the REST library that I’m most familiar with, is lovely. Its clever use of Haskell …

Late last year, as part of my work at Weaveworks, I published grafanalib, a Python DSL for building Grafana dashboards.

We use it a lot, and it’s made our dashboards much nicer to maintain. I’ve written a blog post about it that you can find it on the …

If you want to write a web API in Haskell, then you should start by using my new cookiecutter template at https://github.com/jml/servant-template. It’ll get you a production-ready web service in 5 minutes or less.

Whenever you start any new web service and you actually care …

If “technology is stuff that doesn’t work yet”[1], then patterns are code we don’t know how to write yet.

In the Go Programming Language, the authors show how to iterate over elements in a map, sorted by keys:

To enumerate the key/value pairs in order, we …

Many people are quite comfortable writing ordinary unit tests, but feel a bit confused when they start with property-based testing. This post shows how two ordinary programmers started with normal Python unit tests and nudged them incrementally toward property-based tests, gaining many advantages on the way.

Background

I used to …

A couple of weeks ago I went to the Haskell eXchange in London. I learned a lot and had a great deal of fun while I was there, and went away with my head spinning.

On the weekend after the conference, they had a hack session on Haskell infrastructure. I …

Here’s a quick reference for getting set up to debug Python with gdb, aimed at Debian and Ubuntu users.

Although I’d love to make this a full-fledged write up, it’s going to have to be a note to my future self for now.

It assumes you have …

Bazel is a build tool from Google that I used a lot during my time there. Happily, it’s been open sourced, and so I can look into using it for my own Python projects.

Let me tell you why I’m excited about it, and then follow up with …

https://jml.io/test-docstrings/.

I’ve made my old Google+ post on writing docstrings for tests available on this blog.

It’s a short, five-step guide to writing helpful docstrings for your tests.

Happy hacking!

Ivanka from Coupofy.com has graciously translated my old article, Your Code Sucks and I Hate You into Russian. Nice!

I really should be over this by now.

Here’s how you test exceptions in Python 2.7 and later:

with self.assertRaises(SomeException) as cm:
    do_something()

the_exception = cm.exception
self.assertEqual(the_exception.error_code, 3)

(as recommended in the unittest documentation)

Here’s how you test exceptions in earlier Pythons …